The title announced as last month's top comic book wasn't actually the winner.

What was the best-selling comic book last month? The answer turns out to be slightly more complicated than might be expected.

At the beginning of each month, Diamond Comic Distributors releases sales information for the most popular titles of the preceding month. The company has an all-but-monopoly on comic distribution, thanks to exclusive periodical deals with publishers like Marvel, DC and Image Comics for the "direct market" of comic book specialty stores, which makes up the vast majority of comic sales.

Diamond's information doesn't reveal specific sales figures, but instead gives three rankings: the 300 best-selling comics of the month, ranked by orders from North American comic book stores; a ranking of comic book publishers by unit share based on comics ordered in that particular month; and a ranking of comic book publishers by dollar share, again based on comics ordered in that particular month. This information — which is incomplete, lacking specific sales figures and only including orders to stores of print comics in the North American market, leaving out all international orders and any sell-through information — is, nonetheless, the clearest picture any industry observers have about the behavior of the comic book market.

There is a workaround to the lack of specific sales figures: Each title in the order ranking is given a number, which denotes how that particular comic behaved in respect to a "control" title (traditionally DC Entertainment's Batman series). While DC does not release specific sales numbers for Batman (most publishers keep specific sales figures a secret, for obvious reasons), enough information has been released historically by creators and smaller publishers that rough sales data can be estimated.

Got all that? Good. Here's where things get stranger.

According to Diamond, the best-selling comic book of April was Marvel Entertainment's Secret Empire No. 0, the first issue of the culmination of the company's controversial storyline that recasts Captain America as part of the fascist Hydra organization. That was a big deal for the beleaguered Marvel, which has seen its sales fall over the last year or so, and a big win in the same month as the launch of DC's "The Button" storyline, which advances a plot element from last year's best-selling DC Universe: Rebirth in both the Batman and The Flash series. Secret Empire writer Nick Spencer celebrated the news on Twitter:

There we go. Retailers and readers-- thank you, thank you, thank you for making SECRET EMPIRE 0 the best-selling comic of April 2017!

There's just one problem: Secret Empire wasn't actually April's best-selling comic. It wasn't even the second best-seller of the month.

The confusion comes from the fact that both Batman No. 21 and The Flash No. 21 were offered with different covers. This should come as no surprise, as most high-profile superhero comics are released with multiple covers these days; Secret Empire No. 0 has four covers, for context. In the cases of Batman and The Flash, however, one cover of each was a lenticular cover, and as such cost a dollar more and had to be ordered separately — meaning that Diamond counted those covers as entirely different comic books altogether. (Traditionally, Diamond adds all variant covers together, as they're under the same price point; that's what happened for Secret Empire.)

Looking at Diamond's chart for April's comics, Batman No. 21 logged in at second place on the chart for its lenticular cover, and at seventh place on the chart for its non-lenticular covers. The Flash No. 21 came in at fifth place (lenticular) and 11th place (non-lenticular). John Jackson Miller crunched some numbers at his Comichron website to come up with estimated figures for each of these titles. According to his math, Secret Empire hit North American orders of 162,718, but combined Batman orders were 219,472, and combined Flash orders were 174,803.

In other words, Batman was ordered higher than Secret Empire by close to 57,000 copies ... which is higher than April's entire North America orders for, say, the first issue of Marvel's new Deadpool vs. The Punisher series (45,509 copies ordered for North America, estimated).

Of course, those numbers are just imperfect guesses. But it's clear that the issue declared the most ordered for the month was, in fact, the third-most-popular title for April, thanks to what amounts to a classification decision that awarded bragging rights to the wrong party. Nevertheless, Marvel can celebrate its best month in some time, with Secret Empire joined by two other titles from the publisher — X-Men Gold No. 1 and X-Men Blue No. 1 — ordered in an amount estimated above 100,000 copies, the first time since October 2016 that the company can claim that many 100K-plus comics in one month. Perhaps if it adds some lenticular covers, it might actually be able to take the top spot for real soon.